京都大学 / 新制・課程博士 / 博士(工学) / 甲第23210号 / 工博第4854号 / 新制||工||1758(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 白石 誠司, 教授 木本 恒暢, 教授 引原 隆士 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The goal of this dissertation is to introduce my study on exotic materials in two dimensional world, not only to the well-trained researchers in this field but also to the beginners of condensed matter experiment. I hope this material to be a good guide for those of who paves the way of spintronics and valleytronics The first chapter will give you the introduction to two dimensional materials - Graphene and Monolayer Transition Metal DiChalcogenide (TMDC). The second chapter introduces some toolkits on optical techniques on condensed matter experiment, from very basics for everyone to the advanced for main projects of this work. They include Reflection Contrast, Raman Spectroscopy, Photoluminescence, and Pump Probe Spectroscopy. Chapter three will be review on several literature which are prerequisites for understanding and getting inspiration for this work. They are on the spin-valley indexes of carriers in TMDC, interlayer charge transfer in TMDC heterostructre, valley Hall effect, etc. Chapter four will focus on the first half of main project, “Charge and Spin-Valley Transfer in Transition Metal Dichalcogenide Heterostructure”. Starting from the fabrication of heterostructure samples for our playground, we investigate the Interlayer Charge Transfer in our Heterostructure sample by ultrafast pump probe spectroscopy. We bring the polarization resolved version of the technique to study the Spin-Valley indexes conservation in the interlayer transferred charge, and analyze its physical meaning. We study which one is the dominantly preserved quantity among spin and valley by using the broadband pump probe spectroscopy which covers A and B excitonic energy in TMDC material. As all the measurement here are taken under room temperature condition, this work paves the way for possible real device application. Chapter five will cover the second half of main project, “Electrical control of spin and valley Hall effect in monolayer WSe2 transistors near room temperature”. Valley Hall effect device in praevious studies will be briefly revisited, and our new device is presented, using hole as carrier rather than electron for the robustness of valley index conservation, followed by optical experiment setting and results. Quantitative analyze on valley polarized carrier concentration and its depolarization time constant will follow. Chapter six will be a summary and direction to the future work.

The unique physical properties and low temperature solution processability of organic semiconductors have enabled many applications such as light emitting diodes, flexible logic and solar cells, they are unexploited in their potential for use in solid state devices for spintronics and spin-based information processing. Organic semiconductors composed of mainly light elements appeal to the field of spintronics due to their long spin lifetime originating from their weak spin-orbit coupling. The significant progress in improving carrier mobility of organic semiconductors in the past decade may lead to organic spin transport materials with both long spin diffusion length and spin lifetime which is important for spintronics applications. This dissertation explores the spin transport in organic semiconductors using a variety of experimental techniques from all electrical spin injection and detection to ferromagnetic resonance spin pumping and ISHE spin detection. Non-local spin valves and novel all electrical spin transport device architectures based on high mobility conjugated polymers were studied systematically. The intrinsic roadblocks for electrical spin injection-based measurements were identified as the current spreading effect (electrical cross-talk between the injector and detector electrodes) and the hopping conduction in organic semiconductors which makes all electrical nonlocal spin injection and detection measurements extremely challenging if not impossible for organic semiconductors. In addition, spin current transmission in the out of plane direction of organic semiconductors was studied by tri-layer spin pumping technique where the spin transport properties of organic semiconductors are correlated with their molecular structure and charge transport properties. Spin pumping, a charge-free spin injection method together with ISHE spin detection successfully overcome the impedance mismatch problem and the intrinsic roadblocks imposed by electrical spin injection-based techniques and enabled lateral spin current transport in organic semiconductors to be detected electrically. The lateral spin diffusion length of up to a micrometre was observed in doped conjugated polymers in agreement with theoretical calculations based on exchange mediated spin diffusion model and parameters obtained from first principle. Moreover, this non-local spin transport device structure provides a platform for studying spin transport in a wide range of organic semiconductors where the spin current propagates along the high mobility direction and could potentially be used as building blocks for high performance flexible spintronics devices.

Includes bibliographical references (p. 44-48).

The properties of functional materials have been studied with density functional theory. The first type of materials that have been investigated is the so called diluted magnetic semiconductors. It is a new class of materials that could offer enhanced functionality by making use of spin in addition to the charge of the electron. (Mn,Al) co-doped ZnO has been investigated regarding the Al significance on ferromagnetic behavior using density functional theory within the generalized-gradient approximation plus on-site Coulomb interaction. Despite the presence of Al the system always shows antiferromagnetic behavior. The role of intrinsic defects on ferromagnetism in pure and Cr doped In2O3 was also studied. For pristine In2O3, In vacancy and O interstitial states are completely spin polarized. Moreover, these hole states will create Cr ions in mixed valence state, giving rise to a strong ferromagnetic coupling. The second type of functional materials studied are hydrogen storage materials for mobile applications. These materials are considered as alternative if hydrogen is to replace fossil fuels as a energy carrier. In the view of this a series of compounds containing boron, nitrogen and hydrogen has been examined with respect to electronic structure, dehydrogenation energy and hydrogen diffusion properties. One compound, NH3BH3, has many desirable properties as a hydrogen storage material. In an effort to improve those properties, one of the H atoms in the NH3 group was replaced by Li, Na or Sr. The calculated hydrogen removal energies of the hydrogen release reactions were found to be significantly improved. Finally, a coating material, Al2O3, for wear resistant coatings on high performance cemented carbide cutting tools has been investigated. Chemical vapor deposition grown Al2O3 has been used for decades by the industry. To improve the growth process H2S is added to the gas mixture. The catalytic effect of H2S on the AlCl3/H2/CO2/HCl chemical vapor deposition process has been investigated on an atomistic scale. By applying a combined approach of thermodynamic modeling and density functional theory it seems that H2S acts as mediator for the oxygenation of the Al-surface which will in turn increase the growth rate of Al2O3.

Thesis (Ph.D.)--University of Melbourne, School of Physics, 2008. / Typescript. Includes bibliographical references (leaves 109-122).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 102-114) Also available in print.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Peng Xiong, Florida State University, College of Arts and Sciences, Dept of Physics. Title and description from dissertation home page (viewed Jan. 18, 2005). Includes bibliographical references.

Thesis (M.E.E.)--University of Delaware, 2007. / Principal faculty advisor: Ian Appelbaum, Dept. of Electrical and Computer Engineering. Includes bibliographical references.